In a video tape recorder (hereinafter referred to as a VTR), video signals and audio signals are recorded or played back on/from a magnetic tape using a rotary head. Therefore, the rotary head is provided at a rotary substrate side of a rotary drum. As well known, a rotary transformer is used to transmit signals to this rotary head from a stationary circuit substrate section or from the rotary substrate section to the stationary substrate section, Recently, the functions of VTRs have been improved so that there are those VTRs which are capable of performing not only regular recording/playback operations simply using two rotary heads but also trick plays-provided with many rotary heads. In addition, such a system has been developed not only for recording/playback of video signals by a video rotary head but also for audio signal recording/playback on the same tracks as video tracks-.
As a result, rotary transformers provided with many transmission channels are in use and costs have become expensive, resulting the increase of the costs of the entire VTR sets. In addition, as various rotary heads have become selectable according to VTR specifications, rotary transformers have been demanded to have corresponding specifications and the number of models have increased, impeding their standardization.
To solve such problems, a new system has been developed to reduce the number of channels of a rotary transformer and to standardize rotary transformers by incorporating amplifiers for amplifying playback signals of the heads, a head selector switch for selecting over these amplifiers and a recording system distribution switch on a rotary substrate in the rotary drum,
For instance, a system has been proposed at the ICCE (IEEE International Conference on Consumer Electronics) held on Jun. 6, 1990. In this system, a head switching signal for controlling a head selector switch provided on the rotary head section and such mode information as recording, playback, etc. are multiplexed and transmitted to the rotary head section through a single channel. That is, the head switching signal edge information is FM modulated and this FM wave is AM modulated to a single channel signal according to the mode information, making it possible to transmit a plurality of control signals through the single channel.
There are two head switching signals, i.e., a video head switching signal VSWP for switching the video head channels CH1 and CH2 and an audio head switching signal ASWP for switching the audio head channels CH1 and CH2. Normally, the mutual phase relation of these selector signals VSWP and ASWP is always kept constant. Further, when a control by a well known double azimuth four heads system is performed, a head amplifier switching signal HASW for switching a pair of SP heads and a pair of EP heads also becomes necessary. When a trick play in the SP mode is carried out by paying attention to this amplifier switching signal, the phase of this amplifier switching signal is variable. In addition, as mode information, not only the recording mode and the playback mode but also a trick play mode, head configuration information, etc. become necessary.
However, according to a conventional multiplexed signal transmission system, FM waves are AM modulated according to mode information, but the resolution of AM modulation level is restricted on the system, and thus the multiplexing becomes difficult. Therefore,at most only binary mode information showing the playback mode can be transmitted and the system is inferior in expandability. Further, the phase of the head amplifier switching signal HASW varies at a potential level as described above, and a means for transmitting such phase information simultaneously with this signal is demanded. Furthermore, if an FM demodulator at the rotary head section fluctuates, the DC level after demodulated may fluctuate and a malfunction can result.
As described above, a conventional rotary head amplifier system is restricted in transmission of many control signals and inferior in flexibility and therefore, a system which is capable of transmitting many kinds of control signals and providing a stable and efficient operation has been demanded.
Further, a video multi VTR with a head having almost same width as the track pitch (19.mu.) (hereinafter referred to as a narrow head) added in order to further promote a picture quality in the three-times mode (EP mode) and a Hi-Fi multi VTR (two kinds of paired Hi-Fi heads are required to satisfy the VHS Hi-Fi standard) which is capable of high fidelity recording/playback of all television signals of NTSC/PAL/SECAN color televisions systems have been proposed in recent years. In such VTRs it becomes an important factor that many kinds of control signals described above can be transmitted accurately in less channels to the rotary head section.
However, the multi-head system has not been sufficiently carried out fop a conventional rotary head amplifier system. For instance, in the case of a Hi-Fi VTR, it is necessary to reduce switching noise which is generated when switching a narrow head and an EP normal head, that is, the system switching of multi-head system but no countermeasure was carried out for reducing switching noise.
Here, a general consideration of a method for reducing head system switching noise of a multi-head system will be explained with reference to a video multi system.
FIG. 4(A) shows an example of the head arrangement of a video multi system. A1/A2 are Hi-Fi heads, Sl/E2 and S1/E1 are conventional double azimuth four-heads, and N1/N2 are EP narrow heads. A timing chart for changing the head system from, for instance, E1 to N1 in this system is shown in a set of waveforms in FIGS. 4(B). In FIGS. 4(B), waveform (a) is a Hi-Fi head switching signal ASWP, waveform (b) is a video head switching signal VSWP, waveform (c) is an equivalent EP head switching signal EPSWP, waveform (d) is a narrow head switching signal and waveform (e) is a head system switching information. In these timing charts of FIG. 4(B), if the head system is switching during the indicated overlap period, head switching noises can be almost suppressed without causing the lack of playback signals as both E1 and N1 are kept in contact with a recording tape. In the rotary head amplifier system it is also necessary to transmit head system switching information to the rotary section during the similar period but no countermeasure has been made.
As described above, a conventional rotary head amplifier system is restricted in transmission of many control signals and inferior in flexibility and therefore, a system which is capable of transmitting many kinds of control signals and providing a stable and efficient operation has been demanded.
Further, when the rotary head amplifier system is applied to a multi-head VTR, if it is intended to transmit a head system switching information in addition to various switch selector signals and mode information, no sufficient measure has been provided to set the timing for the switching at a position where no noise is generated.